<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var x=200
        var y=100
        console.log(x+=y);//x=x+y=300
        console.log(x-=y);//x=x-y=200
        console.log(x*=y);//x=x*y=20000
        console.log(x/=y);//x=x/y=200 
    </script>
</body>
</html>